1. Technical Field
The present invention relates to a shrinkable protection element for covering filiform items, e.g. for covering a joint between two electrical cable-ends, said element including a first and second sleeve, both sleeves being elastically expandable in radial direction, being coaxially superimposed each upon the other and being made of compounds of cross-linked polymeric material for surrounding said joint in a radial elastically expanded condition, the first sleeve which is radially inside the second sleeve being electrically insulating at least for a part of its thickness.
2. Discussion of Related Art
Such a shrinkable protection element for cable joint is already known in the art, e.g. from the European Patent EP-B1-0 379 056 (PIRELLI CAVI, S.p.A.). Therein, the residual deformation of the second sleeve, after an imposed elongation applied in time, is smaller than that of the first sleeve. As a result, the risk of permanent deformation may be avoided and a good tightness against possible infiltration of moisture traces may be obtained. It is to be noted that the compound of cross-linkable polymeric material constituting the first sleeve of the protection element includes terbutylperoxy, while the compound of cross-linkable polymeric material constituting the second sleeve includes dicumyl peroxide. These compounds, both including a peroxide-cured Ethylene Propylene Diene Monomer material, hereafter called EPDM, that combine good electrical and mechanical properties. However, a problem with these compounds is that a relatively long time is required before the sleeves reach their final dimensions after stress relaxation, especially at low temperatures.
The above properties are therefore sometimes not applicable to applications which require a quick availability of the cables, i.e. a quick "mise en service". In such applications, it may be possible that the cables have to be available for use after about 30 minutes following the installation of the shrinkable protection element thereon, where in case the known shrinkable protection is used it takes many hours.